Abstract

High-risk human papillomaviruses (HPVs), such as HPV-16, are the etiological agents of squamous cell carcinomas (SCCs) of the anogenital tract and a subset of oropharyngeal cancers. High-risk HPVs encode two oncoproteins, E6 and E7, which promote unscheduled host cell proliferation by targeting the p53 and pRB tumor suppressor proteins, respectively. HPV-16 E7 has been shown to stimulate structural chromosomal instability and DNA breakage. These findings raise several important questions. First, how does HPV-16 E7 induce DNA damage? Second, what are the precise consequences of HPV-16 E7-induced DNA damage for host cell genomic integrity, and lastly, how do HPV-16 E7-expressing cells maintain proliferation despite activated DNA damage checkpoints? Here, we show that HPV-16 E7 activates the Fanconi Anemia (FA) pathway, a branch of the host cell DNA damage response that primarily responds to stalled DNA replication forks. Importantly, we show that HPV-16 E7 expression in FA-deficient cells accelerates the formation of structural chromosomal alterations, which may help to explain the heightened susceptibility of FA patients to HPV-associated tumors. However, we also provide evidence that HPV-16 E7-induced FA pathway activation in FA-proficient cells may contribute to evasion of anti-proliferative host cell barriers by promoting alternative lengthening of telomeres (ALT). Finally, we demonstrate that HPV-16 E7 circumvents DNA damage checkpoint control and promotes aberrant mitotic entry by increasing the proteolytic turnover of claspin, which plays a role in the ATR/CHK1-mediated replication stress response. Collectively, our results underscore that HPV-16 E7 interferes with host cell genome integrity by inducing DNA replication stress. The detrimental effects of HPV-16 E7 on the genomic integrity of host cells with a deficient FA pathway support the notion that this DNA damage response pathway is crucial to prevent HPV-16 E7-induced genomic instability and malignant progression. However, we also provide evidence that HPV-16 E7 can exploit the FA pathway to promote cellular immortalization. Future experiments to explore these events for cancer therapy and/or prevention are warranted.